The Telecommunications Industry Association (TIA) and the Electronics Industry Association (EIA) from time to time promulgate non-binding technical standards for equipment sold in the telecommunications industry. While compliance with these standards by product manufacturers is generally voluntary, the practical importance of producing equipment in compliance with TIA/EIA standards is becoming increasingly important. In addition, the Federal Communication Commission (FCC) from time to time publishes binding regulations governing the telecommunications industry to ensure safety, compatibility, and to minimize problematic interference among various electrical devices and components sold in the telecommunications industry.
In particular, Part 68 of the FCC Guidelines, incorporated herein by this reference, relates to such matters as, for example, the requirement that telephones and other telephone devices be electrically isolated from the telephone network to prevent shock, fire, and other environmental hazards from effecting the users of such equipment. In this context, the term "telephone device" can refer to telephones, modems, personal computers (PCs), fax machines, telephone answering machines (TAM), and the like, which are typically connected to a telephone line through a conventional RJ-11 telephone jack.
Recently, TIA/EIA Standards Proposal No. 3131-A was approved and published as TIA/EIA-695 which relates to, inter alia, various functions to be supported by data access arrangement (DAA) devices, also commonly referred to as direct access arrangement devices. In particular, a DAA is a device which connects a telephone device, e.g., a modem, to an RJ-11 type jack, to thereby provide an interface between the modem and the Public Switched Telephone Network (PSTN). The DAA suitably includes an appropriate opto-electric or other isolation device to isolate the PSTN (which typically operates in the range of 42-200 volts) from the modem (which typically operates in the range of about 1 to 3 volts peak to peak). The transformer circuit within the DAA which performs this voltage step-down function is often referred to as the primary transformer, or simply as a "T1" device.
One of the principle functions of a conventional DAA surrounds the ability of the DAA to detect an incoming ring signal. When a ring signal is detected in a conventional telephone handset, the user can simply lift the telephone handset from the receiver, whereupon the telephone is said to go "off hook". Upon assuming the off hook position, the "off hook" relay within the DAA closes, thereby establishing a connection between the telephone handset and the telephone device which generated the incoming call. When the telephone call is finished and the user places the handset back onto the receiver, the handset is said to go back on hook, whereupon the off hook relay within the DAA is open, terminating the connection.
In a modem context, upon detection of a ring signal, the DAA may be configured to transmit a ring detect signal to a controller associated with the modem or with the PC with which the modem is associated, whereupon a control signal is applied to the DAA's off hook relay, closing the relay. Upon closure of the off hook relay, a data communications path is established between the modem and the telephone device which generated the incoming call.
Many modems in use today, particularly modems associated with PCs, also include a local handset connection, such that both the data modem and the telephone handset are connected to the telephone network through a single, shared RJ-11 phone jack or other interface device. In this context, it will be understood that the term "telephone handset" can include audio speakers, a headset, a voice activated speaker phone, a condenser microphone, or virtually any other audio configuration which permits voice or audio transmission. Moreover, it will also be understood in the context of the present invention that the term "local handset" or "local device" refers to a telephone or other device which shares a common RJ-11 type device with a modem, whereas the term "extension handset" or "extension device" refers to a telephone device which is connected to a common telephone line (for example, in another bedroom of the same home) but which has its own RJ-11 type phone jack (i.e., the extension telephone device does not share a common RJ-11 connection).
DAAs for use with a modem having a local handset are generally well-known, for example as described in Chapter 6 of the "K-Series Design Manual" published by Silicon Systems, the entire disclosure of which is hereby incorporated by this reference. Presently known DAAs, however, are unsatisfactory in several regards. For example, while a presently known DAA associated with a modem may detect an extension telephone device off hook condition while the modem is off hook, many known DAAs are unable to detect an extension device off hook condition while the modem is on hook. Moreover, to the extent a presently known DAA is able to detect when an extension device goes off hook while the modem associated with the DAA is on hook under certain circumstances, the DAA is unable to ascertain when the extension device goes back on hook.
A full featured DAA which overcomes the shortcomings of the prior art is thus needed.
The present invention provides a full-featured DAA for use with a modem which overcomes many of the shortcomings of the prior art.